git-jump: pick a mode automatically when invoked without arguments

When `git jump` is invoked with no positional arguments (and no
arguments after `--stdout`) it currently prints usage and exits with
status 1.

But there are two situations where we can usefully infer the most
valuable and likely mode that a user would want to use, and select it
automatically:

1. When there are unmerged paths in the index, the user likely
   wants `git jump merge`.

2. When the working tree has unstaged changes, the user likely
   wants `git jump diff`.

In this commit we teach `git jump` a new "auto" mode which detects these
cases and dispatches to the corresponding mode automatically. The user
can either explicitly spell out `git jump auto`, or just leave it at
`git jump` (because "auto" is the default).

If none of the interesting cases listed above applies, then auto mode
falls back to the existing usage-and-exit behavior.

Signed-off-by: Greg Hurrell <greg.hurrell@datadoghq.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/git-jump/README

@@ -75,8 +75,20 @@ git jump grep foo_bar
 # arbitrary grep options
 git jump grep -i foo_bar
 
+# jump to places with conflict markers or whitespace errors
+# (as reported by `git diff --check`)
+git jump ws
+
 # use the silver searcher for git jump grep
 git config jump.grepCmd "ag --column"
+
+# pick a mode automatically: "merge" if there are unmerged paths,
+# "diff" if the worktree has unstaged changes, "ws" if there are
+# whitespace problems; otherwise show usage
+git jump auto
+
+# with no explicit mode and no args, same as "auto"
+git jump
 --------------------------------------------------
 
 You can use the optional argument '--stdout' to print the listing to

contrib/git-jump/git-jump

@@ -3,9 +3,11 @@
 usage() {
 	cat <<\EOF
 usage: git jump [--stdout] <mode> [<args>]
+   or: git jump [--stdout]
 
 Jump to interesting elements in an editor.
-The <mode> parameter is one of:
+The <mode> parameter is one of the following.
+With no <mode> and no <args>, it defaults to "auto".
 
 diff: elements are diff hunks. Arguments are given to diff.
 
@@ -16,6 +18,10 @@ grep: elements are grep hits. Arguments are given to git grep or, if
 
 ws: elements are whitespace errors. Arguments are given to diff --check.
 
+auto: select one of the other modes based on worktree state;
+      "merge" if there are unmerged paths, "diff" if there are
+      unstaged changes, "ws" if there are whitespace errors.
+
 If the optional argument `--stdout` is given, print the quickfix
 lines to standard output instead of feeding it to the editor.
 EOF
@@ -82,6 +88,21 @@ mode_ws() {
 	git diff --check "$@"
 }
 
+mode_auto() {
+	if test "$(git rev-parse --is-inside-work-tree 2>/dev/null)" != "true"; then
+		usage >&2
+		exit 1
+	fi
+	if test -n "$(git ls-files -u "$@")"; then
+		mode_merge "$@"
+	elif ! git diff --quiet "$@"; then
+		mode_diff "$@"
+	else
+		usage >&2
+		exit 1
+	fi
+}
+
 use_stdout=
 while test $# -gt 0; do
 	case "$1" in
@@ -99,8 +120,7 @@ while test $# -gt 0; do
 	shift
 done
 if test $# -lt 1; then
-	usage >&2
-	exit 1
+	set -- auto
 fi
 mode=$1; shift
 type "mode_$mode" >/dev/null 2>&1 || { usage >&2; exit 1; }